(1) Field of the Invention
The present invention relates to methods used to form semiconductor devices, and more specifically to a method used to form a barrier layer in a high aspect ratio contact hole, to protect an underlying metal silicide layer from processing conditions used during deposition of an overlying refractory metal layer.
(2) Description of Prior Art
The use of metal silicide layers, located overlying conductive regions in a semiconductor substrate and underlying metal interconnect structures, has allowed decreased metal line resistance, and thus improved semiconductor device performance to be realized via the reduction in performance degrading resistance--capacitance (RC), values. However the use of sub-quarter micron features, used with aggressive semiconductor device designs, have resulted in the creation of high aspect ratios contact holes in insulator layers, which can create problems when attempting to form metal silicide layers, on conductive regions, exposed at the bottom of these high aspect ratio contact holes. The ability to form a metal silicide layer, and an overlying barrier layer needed to protect the metal silicide layer from subsequent process steps such as deposition of a refractory metal layer, becomes more difficult as the aspect ratio of the contact hole increases. This invention will teach a novel method of forming these layers in deep, narrow diameter, contact holes, via directionally implanting the metal component needed for both the metal silicide layer, and overlying barrier layer, directly into a conductive region of the semiconductor substrate, exposed at the bottom of the contact hole. Prior art such as Lee et al, in U.S. Pat. No. 5,552,340, describe a method of forming a barrier layer, overlying a metal silicide layer, located at the bottom of a contact hole, via vapor deposition of the metal layer needed for both silicide and barrier formation. The metal deposition procedure used in this prior art, in addition to difficulties encountered with uniform deposition at the bottom of high aspect ratio contact holes, also results in deposition of metal on the sides of the contact hole which either has to be subsequently remove, or remains to limit the space in the contact hole to be occupied by a low resistance metal plug structure. The present invention however offers the advantage of directionally placing the metal source at the bottom of a high aspect ratio contact hole, without metal being formed on, and than having to be removed, from the sides of the contact hole.